1. Field of the Invention
The present invention relates to radio communication apparatus and system involved in a cognitive radio communication system in which a communication scheme is changed according to an environment.
2. Description of the Related Art
Conventionally, in order to solve a problem that receiving performance of the radio communication apparatus is decreased due to a noise generated by a digital signal processing unit included in the radio communication apparatus, for example, JP-A 2006-191315 (KOKAI) discloses a technique in which a clock frequency supplied in digital signal processing is changed such that the noise generated by the digital signal processing device does not overlap a receiving frequency of the radio communication, and JP-A H9-289527 (KOKAI) discloses a technique in which the clock frequency is temporally changed to perform FM modulation to a clock signal, thereby suppressing an interference signal generated by spread.
However, the noise generated by digital signal processing unit or electronic device is frequently observed in a frequency band used in the communication. Recently, frequency resources have become tight because various kinds of communication are performed. Therefore, the clock is hardly changed in the digital signal processing so as to avoid all the bands used in the communication. Additionally, from the standpoints of circuit scale and cost, it is impractical that a circuit (such as PLL and a control circuit) for changing the clock frequency of the digital signal processing is mounted on all the digital signal processing circuits in introducing the above-described conventional techniques.